“Reserve your right to think, for even to think wrongly is bette“Reserve your right to think, for even to think wrongly is better r than not to think at all. To teach superstitions as truth is a mthan not to think at all. To teach superstitions as truth is a most ost terrible thing.”terrible thing.”

-- HypatiaHypatia

Bit of Administration ….Bit of Administration ….•• ReadingReading

–– Bless, Chapters 3Bless, Chapters 3--66–– BDSV pp. 56BDSV pp. 56--7373

•• Portfolio AssignmentPortfolio Assignment

–– The goal of your portfolio is for The goal of your portfolio is for youyou to demonstrate your achievement of:to demonstrate your achievement of:

Knowing the sky and the Solar System as a part of your envKnowing the sky and the Solar System as a part of your environment to which you are connected ironment to which you are connected –– physically, physically, historically, and culturally/personally.historically, and culturally/personally.

–– The portfolio should include 5 documents demonstrating your learThe portfolio should include 5 documents demonstrating your learning in these dimensions:ning in these dimensions:

•• 1) A cultural connection to the sky; you are encouraged to expl1) A cultural connection to the sky; you are encouraged to explore nonore non--European cultures.European cultures.•• 2) A connection of Newton’s laws of motion and/or gravity to ex2) A connection of Newton’s laws of motion and/or gravity to experiences in your life.periences in your life.•• 3) A connection of the physics of light to experiences in your 3) A connection of the physics of light to experiences in your life.life.•• 4) A connection of the Sun’s energy to your life, or the impact 4) A connection of the Sun’s energy to your life, or the impact of the Second Law of Thermodynamics.of the Second Law of Thermodynamics.•• 5) Your connection to the larger evolutionary processes of the 5) Your connection to the larger evolutionary processes of the Earth and Solar System.Earth and Solar System.

–– Due April 28; you are encouraged to submit your first documents Due April 28; you are encouraged to submit your first documents for review and grading for review and grading before then in order to develop your skills in advance of doing before then in order to develop your skills in advance of doing the entire portfolio.the entire portfolio.

Earliest CivilizationsEarliest Civilizations

Early Greek AstronomyEarly Greek Astronomy•• Plato 400 BCPlato 400 BC

–– Geometric Ideals Geometric Ideals Underly Underly RealityReality•• Uniform Circular MotionUniform Circular Motion

–– Circular Motion at Constant SpeedCircular Motion at Constant Speed–– “No beginning, no end, no change”“No beginning, no end, no change”–– Construct a geometric representation of celestial motions using Construct a geometric representation of celestial motions using

only combinations of uniform circular motions about the only combinations of uniform circular motions about the central fixed earthcentral fixed earth

–– Senses are Imperfect and UnreliableSenses are Imperfect and Unreliable•• Observation is not important Observation is not important -- reason reigns supremereason reigns supreme

–– Qualitative agreement is acceptableQualitative agreement is acceptable

Early Greek AstronomyEarly Greek Astronomy

•• Eudoxus Eudoxus and and Calippus Calippus 400 BC400 BC

Early Greek AstronomyEarly Greek Astronomy•• Aristotle 350 BCAristotle 350 BC

–– Lunar Phases and EclipsesLunar Phases and Eclipses•• Argued that Sun was further than the moonArgued that Sun was further than the moon

–– EclipsesEclipses–– Slower motion in the skySlower motion in the sky

•• Argued that Moon shines by reflected light from SunArgued that Moon shines by reflected light from Sun–– Intellectual leap toward relationships that are independent of EIntellectual leap toward relationships that are independent of Eartharth

–– Spherical EarthSpherical Earth•• Shadow is round during lunar eclipsesShadow is round during lunar eclipses•• Travel in latitude changes the positions of the starsTravel in latitude changes the positions of the stars•• Elephants were found both to the east in India and to the west iElephants were found both to the east in India and to the west in Moroccon Morocco•• Only spherical shape would allow motion to the center to be straOnly spherical shape would allow motion to the center to be straight downight down

–– Motion of EarthMotion of Earth•• Realized that daily motion could be either earth or celestial spRealized that daily motion could be either earth or celestial sphere spinninghere spinning•• Considered heliocentric universe, but rejected because no parallConsidered heliocentric universe, but rejected because no parallax was seenax was seen

–– Cosmology of the SpheresCosmology of the Spheres

Right Reasoning, Right Conclusion!

Wrong Reasoning, Right Conclusion!

Right Reasoning, Wrong Conclusion!

Wrong Reasoning, Wrong Conclusion!

Early Greek AstronomyEarly Greek Astronomy•• Aristotle 350 BCAristotle 350 BC

–– ChemistryChemistry•• Earth, Air, Fire, Water Earth, Air, Fire, Water -- the stuff of the human worldthe stuff of the human world•• Quintessence Quintessence -- the stuff of the celestial bodiesthe stuff of the celestial bodies

–– PhysicsPhysics•• The universe as a machineThe universe as a machine•• All vertical motion driven by inclination to natural places All vertical motion driven by inclination to natural places •• The natural place of Earth was toward the center of the UniverseThe natural place of Earth was toward the center of the Universe/Earth/Earth

–– First theory of gravity!First theory of gravity!

–– Encyclopedic Treatises on Nearly Every FieldEncyclopedic Treatises on Nearly Every Field

For 2000 years the Universe was AristotelianFor 2000 years the Universe was Aristotelian(though primary impact was after 1200 AD)(though primary impact was after 1200 AD)

The Alexandrian SchoolThe Alexandrian School•• Located in Egypt, but center of Greek culture after 330 BCLocated in Egypt, but center of Greek culture after 330 BC•• Conquests of Babylonia by Alexander the Great brought rich Conquests of Babylonia by Alexander the Great brought rich

observational dataobservational data

The Alexandrian SchoolThe Alexandrian School

•• Aristarchus Aristarchus of of SamosSamos 300 BC300 BC

"You King"You King Gelon Gelon are aware the 'universe' is the name given by most astronomers are aware the 'universe' is the name given by most astronomers to the sphere the center of which is the center of the Earth, whto the sphere the center of which is the center of the Earth, while its radius is equal ile its radius is equal to the straight line between the center of the Sun and the centeto the straight line between the center of the Sun and the center of the Earth. This r of the Earth. This is the common account as you have heard from astronomers. Butis the common account as you have heard from astronomers. But Aristarchus Aristarchus has has brought out a book consisting of certain hypotheses, wherein it brought out a book consisting of certain hypotheses, wherein it appears, as a appears, as a consequence of the assumptions made, that the universe is many tconsequence of the assumptions made, that the universe is many times greater than imes greater than the 'universe' just mentioned. His hypotheses are that the fixedthe 'universe' just mentioned. His hypotheses are that the fixed stars and the Sun stars and the Sun remain unmoved, that the Earth revolves about the Sun on the cirremain unmoved, that the Earth revolves about the Sun on the circumference of a cumference of a circle, the Sun lying in the middle of the orbit, and that the scircle, the Sun lying in the middle of the orbit, and that the sphere of fixed stars, phere of fixed stars, situated about the same center as the Sun, is so great that the situated about the same center as the Sun, is so great that the circle in which he circle in which he supposes the Earth to revolve bears such a proportion to the dissupposes the Earth to revolve bears such a proportion to the distance of the fixed tance of the fixed stars as the center of the sphere bears to its surface." stars as the center of the sphere bears to its surface."

»» ArchimedesArchimedes

The Alexandrian SchoolThe Alexandrian School•• Aristarchus Aristarchus of of SamosSamos 300 BC300 BC

–– Relative Distances of Moon and SunRelative Distances of Moon and Sun

E S

M

= cos MESEMES

Earth Sun

The Alexandrian SchoolThe Alexandrian School•• Aristarchus Aristarchus of of SamosSamos 300 BC300 BC

–– Relative Distances of Moon and SunRelative Distances of Moon and Sun•• Requires measuring the angle MESRequires measuring the angle MES•• Suggested measuring time from first quarter to third quarter andSuggested measuring time from first quarter to third quarter and

time from third quarter to first quarter, then taking the ratiotime from third quarter to first quarter, then taking the ratio•• Used 87Used 87oo with no mention of originwith no mention of origin•• Found that the Sun is 20x further than the MoonFound that the Sun is 20x further than the Moon•• But in fact ….But in fact ….

Earth Sun

E S

M

The Alexandrian SchoolThe Alexandrian School•• Aristarchus Aristarchus of of SamosSamos 300 BC300 BC

–– Relative Distances of Moon and SunRelative Distances of Moon and Sun•• Requires measuring the angle MESRequires measuring the angle MES•• Suggested measuring time from first quarter to third quarter andSuggested measuring time from first quarter to third quarter and time from time from

third quarter to first quarter, then taking the ratiothird quarter to first quarter, then taking the ratio•• Used 87Used 87oo with no mention of originwith no mention of origin•• Found that the Sun is 20x further than the MoonFound that the Sun is 20x further than the Moon•• Measurement of angle MES is impossible; Sun is 400x further thanMeasurement of angle MES is impossible; Sun is 400x further than the Moonthe Moon

EarthSunSun

The Alexandrian SchoolThe Alexandrian School•• Aristarchus Aristarchus of of SamosSamos 300 BC300 BC

–– Relative Sizes of Moon and SunRelative Sizes of Moon and Sun

The Alexandrian SchoolThe Alexandrian School•• Aristarchus Aristarchus of of SamosSamos 300 BC300 BC

–– Relative Sizes of Moon and SunRelative Sizes of Moon and Sun•• Sun and Moon are same angle in the sky (0.5Sun and Moon are same angle in the sky (0.5oo))•• Sun is 20x further away than the MoonSun is 20x further away than the Moon•• Sun must be 20x larger than the MoonSun must be 20x larger than the Moon

1

20

Earth

The Alexandrian SchoolThe Alexandrian School•• Aristarchus Aristarchus of of SamosSamos 300 BC300 BC

–– Relative Sizes of Earth, Moon and SunRelative Sizes of Earth, Moon and Sun

Earth

1 32

Time 1Time 10 hr

Time 2Time 21 hr

Time 3Time 33 hr0 hr 1 hr 3 hr

Earth’s Shadow is 3x Diameter of MoonEarth’s Shadow is 3x Diameter of Moon

The Alexandrian SchoolThe Alexandrian School•• Aristarchus Aristarchus of of SamosSamos 300 BC300 BC

–– Relative Sizes of Earth, Moon and SunRelative Sizes of Earth, Moon and Sun•• Found that Sun is 6Found that Sun is 6--7x larger than the Earth, compared to 109x7x larger than the Earth, compared to 109x•• The Sun is larger than the Earth!The Sun is larger than the Earth!•• Led him to suggest a SunLed him to suggest a Sun--centered (“heliocentric”) universecentered (“heliocentric”) universe

Earth

The Alexandrian SchoolThe Alexandrian School•• Aristarchus Aristarchus of of SamosSamos 300 BC300 BC

–– Relative Sizes of Earth, Moon and SunRelative Sizes of Earth, Moon and Sun

•• Found that Sun is 6Found that Sun is 6--7x larger than the Earth, compared to 109x7x larger than the Earth, compared to 109x•• The Sun is larger than the Earth!The Sun is larger than the Earth!•• Led him to suggest a SunLed him to suggest a Sun--centered (“heliocentric”) universecentered (“heliocentric”) universe

"["[CleanthesCleanthes, a contemporary of, a contemporary of AristarchusAristarchus] thought it was the duty of the Greeks to indict ] thought it was the duty of the Greeks to indict Aristarchus Aristarchus ofof Samos Samos on the charge of impiety for putting in motion the Hearth of theon the charge of impiety for putting in motion the Hearth of theuniverse [i.e. the earth], . . . supposing the heaven to remain universe [i.e. the earth], . . . supposing the heaven to remain at rest and the earth to at rest and the earth to revolve in an oblique circle, while it rotates, at the same timerevolve in an oblique circle, while it rotates, at the same time, about its own axis." , about its own axis."

»»PlutarchPlutarch

The Alexandrian SchoolThe Alexandrian School•• EratosthenesEratosthenes 200 BC200 BC

–– The Size of the EarthThe Size of the Earth•• Note that all of Note that all of Aristarchus’ Aristarchus’ results are results are relativerelative sizessizes

From Sun

From Sun

Light rays from very distant objects arrive at every point on Earth from the same direction!

HK

NY

Earth

From Sun

From Sun

7 o

Alexandria

7 o

Syene

Distance around Earth = 360o/7o x Distance Syene to Alexandria= 50 x 5000 stades !

From SunFrom Sun

The Alexandrian SchoolThe Alexandrian School

•• The Size of the Universe, circa 200 BCThe Size of the Universe, circa 200 BC

•• Earth’s DiameterEarth’s Diameter 13,00013,000 kmkm 12,75612,756 kmkm•• Moon’s DiameterMoon’s Diameter 4,3004,300 34763476•• Sun’s DiameterSun’s Diameter 9 x 109 x 1044 1.39 x 101.39 x 1066

•• EarthEarth--Moon DistanceMoon Distance 4 x 104 x 1055 3.84 x 103.84 x 1055

•• EarthEarth--Sun DistanceSun Distance 101077 1.50 x 101.50 x 1088